Control for oxygen producing apparatus



May 22, 1951 s. c. COLLINS ErAL CONTROL FOR OXYGEN PRODUCING APPARATUS Filed June e, 194s l Patented May 22, 1951 y l UNITED s'm'rssl PATENT orales a Samuel C. Collins, Watertown, and Howard 10. McMahon,. Lexington, Mass.; said McMahon assignor to Arthur D. Little, Inc., Cambridge,-

Mass., a corporation of Massachusetts j v Application June s, 194s, serial No. 674,670

' v 13 claims. (c1. sz-2) 1 2 This invention relatesto controls for oxygen heat insulating material such as glass wool. To producing apparatus. p cool down the apparatus compressed air need be The object of this invention is to provide for passed through only one of the heat exchangers the automatic control of the method and apon its way to and from the expansion engine,

paratus of the character disclosed in a copending since in such a limited cycle of flow the expanapplication, Serial No. 661,25-3,led April 11, 1946 sion of the air with the performance of exby Samuel C. Collins. The present invention is ternal work would produce the desired coolingparticularly applicable to such apparatus when down effect. However, since in the subsequent used forl the production of substantially pure liquefaction period it is necessary to produce a oxygen from atmospheric air, to the end that charge of the liquefied constituents of the air, upon being started the performance will proceed We prefer a course of flow of the air which will through the cooling-down and liquefaction periserve the functions of both periods.

' ods and bring about the normal operation to Accordingly during the cooling down period produce oxygen. It is a feature of the invention the air flows through the heat exchangers A and that should any inadvertent interruption occur l5 B and the expander D. Compressed air, prefin the oxygen producing operation, the controls erably at from 150 to 175 pounds per square will act automatically to repeat the starting-up inch (p. s. i.) and at ordinary room temperacycles to restore the system to full operatingr tures, is brought to an air inlet 2 of the apconditions. paratus. This inlet leads to one chamber 4 of a The best mode in which it has been contempair of valve chambers 4 and 6 in each of which plated to apply the principles of the present inis a valve, 8 and I0 respectively, secured to ka vention is shown in the accompanying diagramcommon piston rod I2 which is connected to one matic layout of the preferred arrangement of arm |4a of a bell crank lever I4 pivoted at I6. apparatus but this drawing is to be deemed When the valves 8 and I0 are in the positions merely illustrative for it is intended that the shown the compressed air from inlet 2 passes patent shall cover by suitable expression in the through the chamber 4 into a branch l8a of a pipe appendedclaims whatever features of patentable I8 directly connected between the other chamber novelty exist in the invention disclosed. 4(i and an inner annular passageway 2U of the ex- Referring to the drawing the preferred archanger A. The opening from chamber 6 into rangement of oxygen producing apparatus compipe I 8 is closed by the valve I0 when positioned prises three heat exchangers, A, B and C, an exas shown.

pander D, a fractionating column E, numerous The compressed air flows through the passageconnections, and the several control devices way 20 into a pipe 22 which, together with its which render the performance of the apparatus branch 22a, leads to another pair of chambers entirely automatic throughout what maybe 24 and 26 similar to those already described. termed three rather distinct periods of the over- These contain valves 28 and 30 respectively, havall operation. These periods may be designated ing a common piston rod 32 which connects with as the cooling-down period during which the one arm 34a of another bell crank 34 pivoted various parts of the apparatus are cooled to temat 36. When the lower valves 8 and ID are at peratures suitable for their proper operation, the left ends of their respective chambers 4 and the liquefaction period duringwhich a suicient 6, the upper valves 28 and 30 are at the right charge of liquefied constituents of airis produced ends of their respective chambers 24 and 26. to affect certain controls, and the distillation Accordingly, as shown, the opening from pipe period during which the desired oxygen is gen- 22 to the chamber 24 is closed by the valve 28 erated. The first two periods are transitory, While the Opening IOIn the branch 22a to Chameach lasting about an hour, but the distillation ber 26 is open, as is likewise an opening frOm this period is not one of any special duration for it latter chamber into a pipe 38 leading to a T 40. may go on indenitely so long as the apparatus The compressed air accordingly iOWS thrOllgh is supplied with compressed air. pipe 22, branch 22a, chamber 26 and pipe 33 00 5o the T 40.

The coozmg'down period From one side of this T 40 a pipe 42, contain- This period is solely a preliminary one and ing a valve 44, connects with another T 46 from its purpose is to cool down the apparatus as a which a pipe 48 leads to a surge tank 50. From whole. For clarity of disclosure the various the other side of the T 4I] a tube 52, containing elements of the apparatus are shown in the a manually operated valve 52a, extends to the drawing in a sort of distributed arrangement, upper or colder end of the first heat exchanger but in the actual apparatus the elements are A, forms a coil 52h thereabout and then runs to closely adjacent one another within an overall the T46. During the cooling-down period valve casing. Spaces between the elements and be- 44 is kept wide open and valve 52a is preferably tween them and the casing are packed with good e0 closed so that the air flowing in pipe 38 to the Y 3 Tltwillnowpastthe valve 44 and 1'-40on through pipe 48 to the surge tank 60. This tank.

is connected by a pipe 54 with the inlet 00 to the expander D. The details of this expansion engine are shown in a copending application, Serial No.

665,206, illed April 26, 1946,by Samuel C. Collins.

Suillce it to say here that suitable valves and mechanism are provided which permit the com-` pressed air at approximately its entering pressure of from 150 to 175 p. s. i. to be admitted through the inlet 66 to the cylinder of the engine, to ex-` pand therein against a movable piston and there-` by perform external work, and to be discharged from an outlet 68 at about 5 p. s. i. and at a considerably reduced temperature, the reduction in temperature depending upon the expansionratlo,` the emciency of the engine and to some extent upon its temperature. Y

As before noted herein, the cooled air leaving the expander could return directly to the rst heat exchanger, so far as the purposes of the cooling down period require, but we prefer to have this cooled air entering T 62 to ilow thence along a pipe 64 which contains a pressure actuated control valve 66 and leads to a T 08. While the ap# paratus is cooling down this valve 66 remains open. -From the T 68 the air llows through a pipe 10 into an outer annular passageway 'I2 v through the second heat exchanger B. This passageway 12 is connected by a pipe 14 with the valve chamber 24. 4

With the valves 28 and 30 positioned as shown, the cooled air passes from the chamber 24 intoj one branch 16a of a pipe 'I6 leading to an outer annular passageway 'I8 through the ilrst heat exchanger A. 'Ihe other branch 16h of this pipe I6 is connected to the other valve chamber 26 but its opening thereinto is closed by valve as` shown. The cooled air accordingly passes through .the annular passageway 18 in the rst heat exchanger and thence through a pipe and its branch 80a to the valve chamber 6, whence it is discharged from the apparatus through an out` let 82. Another branch 80h from the pipe .80 leads to the other valve chamber 4 but ilow of the cooled air into this chamber is prevented by the valve 8.

Periodically (about every two minutes) the switch valves 8, I0, 28, and 30 are shifted in their respective chambers by the action of suitable reversing mechanism indicated by the rectangle 84. This is connected by a rod 86 ,with the arm |4b of the bell crank I4 and by anotherrod 68 with the arm 34h of the bell crank 34. The reversing mechanism is driven by a shaft 90 having a 'worm and gear connection 92 with a shaft 94 of the expander D. The purpose of this periodic shifting of the'switch valves has to do with' the cleaning oi' the annular passageways through the` ilrst heat exchanger A and the purification of the air prior to its entry 'into the expander D, of which more will be said later herein.

During the cooling-down period. the entering compressed air is cooled, first by an exchange of; heat with the' cooled air ilowing in the opposite .4 muquelactionperioa During this period the second heat exchangerB acts as a liqueiier to produce a charge of liquened air in the base of the fractionating column E. The air to be thus liquefied is taken from the pipe 88 just beyond lthe first heat exchanger A.

A tube 00 leading from pipe I8 forms a coil a or passageway about the heat exchanger B ingood thermal contact therewith and'thenl runs l to another pressure actuated valve 88 which is responsive to the temperature conditions of the exhaust fluid from the expansion engine. This valve 98 is closed duringfthe cooling down period and normally remains closed after the apparatus enters upon its oxygen producing performance. Despitey its being closed the high pressure air from pipe 08 stands in the eway 96a, and when the temperature of the air passing through the outer annular passageway 'I2 of the second heat exchanger B has reached approximately 103 K. or 274 F. the air in the coil 96a becomes liqueed.

In close thermal contact with the pipe 60, leading from ,the discharge port 68 of the expander, is a bulby l00containing an expansible fluid. This bulb is connected by a tube |02 with the pressure-responsive means of the valve 98. When the air in the coil 96a becomes liquefied the temperature of the air being discharged from the engine will be such as to cool the fluid in bulb |00 to a point where its pressure permits valve 98 to open. This permits the high pressure air in pipe 38 and tube 96 to force the liquid air in the coil 96a past the now open valve 98 into a tube.

|04. This tube hasa restriction winding |04a therein and runs from valve 98 to a T |06. The latter is connected by a pipe |08 with the top of the rectifying column E, the preferred details of which are disclosed in a copending application, Serial No. 676,075, led June 1l, 1946, by Howard O. McMahon. As the liquid air from coil a moves on as just described, more is formed in the coil 96a and in turn passes along 'to the column E. If this flow through tube |04 tends to become so rapid that gaseous air passes along with the liquidk air the bubbles carried into the restriction Winding |04a impede the flow and enable the desired liquefaction of the air in coil 96a to be accomplished.

In due time, usually in about an hour after the liquid air begins to be formed in coil 96a, the col'- lection of this liquid air in the base of the column E reaches a level, indicated by the dotted direction through the rst heat exchanger A and then furtherv cooled by expansion with the performance of external work through the agency oi' the expander D. This cooling proceeds with con-` tinuing fall of temperaturethroughout the whole apparatus for about an hour or an hour and a quarter. By that time the air leaving the expander D and passing through the pipe 64 has reached a temperature of approximately 103 K;

line I |0, at which it can run into a tube H2 leading from the boiler of the rectiiler E to a vaporizing chamber ||4. This chamber should be located where the temperature which affects it externally is such that upon liquid entering the chamber it is vaporized and returned through tube ||2 to the fractionating column. For example, the chamber might be located outside the casing of the apparatus but for convenience it is preferred to place it in thermal contact with the heat exchanger A as shown. Closely associated withthe chamber |I4 is a bulb H6 which is connected by a tube |l8 with the pressure responsive means of the valve 66. This bulb containsan expansible uid whose pressure varies with its temperature. As the liquid from the lbase of the fractionating column flows through tube ||2 into the chamber ||4, the temperature of the wall of the chamber is greatly reduced despite the fact that vapori.

zation of the liquid takes place. As a consequence the duid in bulb ||6 and tube I|8 is cooled to a or 274 F. and initiates the liquefaction period. 7s point where its pressure permits valve 66 to close and cut oif the now of the expander air from the engine D through the pipe 64.

This forces the air leaving the expander to flow through pipe 60 to T 62 and thence through a pipe into a surge tank |22. 'I'he air passes thence through a pipe |24 into an inner annular passageway |26 through the second exchanger B, whence it thenproceeds by a pipe |28 'to a central manifold |30 forming part of the boiler of the fractionating column E. The details of a preferred form of boiler are disclosed in an application for patent, Serial No. 674,521, filed June 5, 1946, now Patent Number 2,494,304, dated January 10, 1950, by Howard O. McMahon. The central inlet manifold |30 is connected by a coil of.

tubes |3| with an outlet manifold |32 which in turn is connected by a pipe |33 with an inner annular passageway |34 through the third heat exchanger C. The air in passing through the coil |3| gives upheat t3 the liquid outside the coil in the boiler and is itself liquefied during this heat exchange action. The liquid air passes on through pipe |33, passageway |34 wherein it is further cooled, and flows thence into a tube |36. The latter contains an expansion device, here represented as a capillary restrictor |36a, and continues on to the T |06. The liquid air is expanded in its passage through the restrictor |36a, and moves on at reduced pressure to the T |06 and thence through the. tube |08 to be distributed in the top of the fractionating column E, wherein the fractionation and distillation of the air takes place.

The resistance to flow offered by the restrictor |36a is'such that it causes the air leaving the expander D through the pipe 60 to assume a pressure of about 70 p. s. i. and a temperature of about 108 K. or 265 F. When this temperature is communicated to the fluid in bulb |00 and tube |02 it eiects the closure of valve 98. This stops the fior-1 of air from pipe 38 through the tube 96 and coil 96a and thus causes all ilow of air to be through the expander D, the second heat exchanger B, the coil of tubes I 3| in the boiler of the fractionating column, and the third heat exchanger C into the top of the column E. This brings the apparatus to full operative setting for the production of oxygen. As noted, all the air is expanded in the engine D with the performance of external work, is liquefied in the 'boiler coil, and is distributed at reducedpressure into the top of the Acolumn E for distillation.

The distillation period The liquid air trickling down through the packing of the column in counter-flow with vapors rising in the column is separated into its constituents. The nitrogen, argon and such other constituents as may be boiled-olf rise to the top of the column while the oxygen passes down as liquid to the bottom about/the coils, gradually displacing the liquid air which was collected there during the liquefaction period. This air is vaporized and passes upward through the co1- umn with some resulting rectification. In due tlmethe space of the column about the coil, |3| becomes filled with liquid which is for the most part oxygen with some nitrogen, argon and perhaps other ingredients present. The latter elements are substantially all eliminated within the boiler proper so that eventually substantially pure oxygen gas enters a tube |38 extending upward within the central manifold |30. This oxygen gas flows through the tube |38 into a central passageway |40 through the second heat ex- 6 changer B and continues on through a pipe |42 to a central passageway |44 in the first heat exchanger A, whence it moves on through pipe |46 to an outlet |48 from which4 the discharge is conl trolled byavalve |50. p

The nitrogen, argon and such other vapors as make up the eiiluent rise in the column E and pass out of the top of the column E through a pipe |62 that leads to an outer annular passageway |54 through the third heat exchanger C. The

efiluent then ilows along a pipe |56 to the T 68 and thence through pipe 'I0 into the annular passageway 'I2 through the second heat exchanger B. From this passageway the eiiluent moves along pipe 'I4 to Valve chamber 24. With the switch valves in the positions shown the eilluent moves on through the branch 16a and pipe 16 into the annular passageway 'I8 through the rst yheat exchanger A and then goes through pipe and branch 80a into chamber 6 whence it escapes from the system through the discharge outlet 82. In all three heat exchangers the direction of now of the eilluent is counter to that of the air stream and in each exchanger heat is taken from the air and absorbed by the eilluent. In exchangers B and A, the counter-flowing stream of oxygen in the central passageways also absorbs some heat from the air.

As earlier noted, once the operation of the apparatus is started the switch valves 8, I0, 28 and 30 are shifted periodically. 'I'he flow of air and of the eilluent when the valves are in the positions shown has already been described. When the several Valves are shifted to the opposite ends of their respective chambers, the entering air will flow from inlet 2 through chamber 4 into branch 80h and thence through pipe 80 into the outer annular passageway I8 through the heat exchanger A, going on through pipe 'I6 and branch 1Gb into chamber 26 from which it passes on to the expander. At the same time the eilluent from pipe I4 enters chamber 24 and flows into pipe 22 and thence through the inner annular passageway 20 of the first heat exchanger. Itgoes on through pipe I8 into chamber 6 to be discharged through the outlet 82.

During the ow of air through the rst heat exchanger, water vapor and carbon dioxide, and possibly other impurities, are deposited on the wall of the passageway and would in time either clog the passageway or adversely affect its flow capacity. By changing the air flow from one annular passageway to the other at frequent intervals these deposits are kept small while forming and then are entirely removed as the eilluent is counter-flowed through the passageway. This reevaporates. sublimes or otherwise removes the water vapor and carbon dioxide and other impurities and all are carried out with the eilluent through the .discharge outlet 82.

In some instances it may occur that the conditions of pressure and temperature which naturally arise in a heat exchanger are not favorable for the complete removal of the deposits. In such cases either the pressure or temperature should be artificially adjusted. One way of doing this is to compress the air to a higherpressure so that the deposits of carbon dioxide form at a higher temperature. Another Way is to recirculate a portion of the compressed air about that region of the rst heat exchanger at which the carbon dioxide deposits occur, after the compressed air has emerged from that heat exchanger and before it has gone to the expansion engine. For example, with valve 52a opened, the

, 7 valve 44 may be set so. that a desired'portlon of the compressed vair flowing from the first heat exchanger is caused to pass through the tube 52 and coil 52h to rejoin the remainder of the air passing through the valve 44. This cooled compressed air nowing in the coil B2b cools the region of the heat exchanger where the carbon dioxide would normally be deposited and causes the deposit to take place nearer to the warmer end of the exchanger where the evaporative capacity of the returning waste gases is amply sufiicient to remove the deposits. In case the functions of coil 52h are not deemed necessary the valve-52a may be closed, thus causing all the air from the rst exchanger to flow directly to the T46.

If low pressure liquid oxygen is desired it may f returning through the tube ||2 into the column.

If for any reason the liquid should inadvertently fall below the level H0, the liquefied constituents of air in the tube 2 and chamber ||4 will be entirely vaporized very promptly. This will permit the temperature of bulb ||6 to rise due to the heat transfer from the first heatexchanger A, causing the fluid therein and in tube ||8 to expand and bring about the opening of valve 66. Air will thereupon again ow through pipe 64 to T 68, join the eiiluent in pipe |56 and move on through pipe 'l0 into heat exchanger B. This willpromptly reduce the temperature of pipe 60 and so affect the uid in bulb |00 and tube |02 that valve 98 will open to permit liquid air y from the passageway 96a about the second heat exchanger B to pass on into the column and ref store the liquid level in the base to that desired.

Upon reaching the level and overowing into chamber ||4 the valve 66 is again closed, and the closure of valve 98 will promptly follow thus automatically restoring the oxygen producing op-A eration of the apparatus. Accordingly, once the distillation period is brought about the controls will maintain the operation of the apparatus for the production of oxygen. even restoring this operative condition if for any reason not anticipated the yield of liquid in the base of the column should be unexpectedly reduced.

After the apparatus is in full operation the pressure'of the incoming air may be lowered if desired, and even with a pressure as low as 100 p. s. i. the oxygen will continue to be produced. It is felt, however, that somewhat more emcient operation takes place when the compressed'air is supplied at a pressure somewhere in the neighborhood of 125 p. s. i. If 100 cubic feet of com.- pressed air at about this pressure and at room temperature is put into the apparatus, then from 10 to 20 cubic feet of substantiallyl pure oxygen gas (99.6% Oz) will be delivered from outlet |48 at approximately room temperature and a pressre of about 5 p. s. i. Under the same conditions of entering'air, the apparatus will produce about 2 kilograms of liquid oxygen (which would be about cubic feet if the oxygen were vaporized) which can be withdrawn from outlet |64 at substantially atmospheric pressure.

We claim:

1. Apparatus forv liqueiying and separating I compressed mixed gases, comprising a heat exchanger wherein said mixed gases are passed in to receive and expand the mixed gases, fractionating means connected to the exhaust of said f engine to receive the expanded mixed gases, conduit ymeans leading V'from said fractionating means to said heat exchanger to providesaid cold fluid thereto, a bypassleading from said exhaust of said engine to said conduit means whereby said expanded mixed gases ow to and through said heat exchanger in'heat exchange relation with said mixed gases, and a thermally actuated control valve in said bypass actuated by liquid formed in said fractionating means, whereby said valve is actuated into closed yposition by the temperature of said liquidto permit all of said expanded mixed gases to flow into said fractionating means.

2. The apparatus of claim 1, wherein the heat exchanger is a recuperative reversing exchanger provided withlvalve means operative to alternate periodically the ows'of the compressed mixed gases and the cold fluid'between two passageways in said exchanger.

3. Oxygen producing apparatus comprising a heat exchanger having passageways for separated flows of fluid one of said passageways being for the introduction of compressed air, an expansion engine connected to thevoutlet end of said incoming air passageway, fractionating and distilling means into which said engine discharges, conduit means leading from said fractionating and distilling means to a. second passageway of said heat exchanger, a bypass leading from the exhaust end of said engine to said conduit means whereby ow of fluidA from the engine passes through the bypass to the heat exchanger to flow therethrough in said second passageway to effect cooling of the incoming compressed air in the first passageway, and a thermally actuated control valve in said bypass actuated by liqueied constituents of air in said fractionating and distilling means whereby said valve is actuated into i closed position by the temperature of said liquened constituents to permit au of the air sewing fromthe engine to pass into the fractionating and distilling means; said valve being actuated intoopen position by said temperature when said temperature is'lappreciably above that ofthe normal boiling point of said liquefied constituents;

4. Oxygen producing apparatus comprising a heat exchanger having passageways for separated ows of uid one of said passageways being for the introduction of compressed air, an expansion engine connectedto the outlet end of said incoming air passageway, fractionating and distilling means into which said engine dis'- charges, conduit means leading from said fractionating and distilling means to a second passageway of said heat exchanger, a bypass leading from the exhaust end of said engine to said con` duitmeans whereby ow of fluid'from the engine passes through the bypass to the heat exchanger to now therethrough in said second passageway to leect cooling of the incoming compressed air inthe first passageway, and a thermallyactuat-v ed control valve in said bypass actuated by liquefied constituents of air in said fractionating and distilling means whereby said valve is actuated into closed position by the'temperature of said liquefied constituents to permit all of the' air flowing from the engine to pass vinto the fractionating and distilling means; said valve being actuated into open position by said temperature when said temperature is appreciably above that of the normal boiling point of said liquefied constituents, and being actuated into closed position by the eifect of said temperature when said temperature is appreciably lower.

5. Oxygen producing apparatus comprising a first heat exchanger having separate thermally bonded passageways in heat exchanging relation one of said passageways being for the introduction of compressed air, an expansion engine havingI its inlet connected to the outlet end of said incoming air passageway, a second heat exchanger having separated thermally bonded passageways in heat exchange relation, one of which passageways is connected with the outlet from said engine and another of which passageways is connected with the inlet of said expansion engine and with a fractionating column beyond said second exchanger, and a thermally actuated valve in the latter passageway responsive to the temperature conditions of the exhaust fluid of said engine; the said valve being opened by the effect of the temperature of said exhaust fluid when said temperature reaches a degree wherein the air in said latter passageway becomes liquid, to permit flow of said liquid air to said column.

6. Oxygen producing apparatus comprising a heat exchanger having passageways for separated flows of fluid one of said passageways being for the introduction of compressed air, an expansion engine connected to the outlet end of said incoming air passageway, a second heat exchanger also having passageways for separated flows of fluid, the rst passageway of said second heat exchanger being connected to the discharge side of said expansion engine, fractionating and distilling means into which said engine discharges during normal operation of the apparatus, and a second passageway of said second heat exchanger being connected to a second passageway of said first heat exchanger, a by-pass extending from the connection between the expansion engine and the second heat exchanger to the second passageway in the second heat exchanger, whereby ow of fluid from the engine passes through the second heat exchanger and returns to the rst heat exchanger to ilow therethrough in one passageway to effect cooling of the incoming compressed air in the other passageway, and a thermally actuated control valve in said bypass responsive to the temperature in the region 0f the first heat exchanger; said valve being held open by a temperature not substantially different from that of said region to permit the air flowing from the engine to pass through the second heat exchanger and return to the first heat exchanger.

7. Oxygen producing apparatus comprising a heat exchanger having passageways for separated flows of iiuid one of said passageways beving for the introduction of compressed air, an

expansion engine connected to the outlet end of saidincoming air passageway, a second heat exchanger also having passageways for separated flows of fluid, the first passageway of said second heat exchanger being connected to the discharge side of said expansion engine, fractionating and distlling means into which said engine discharges during normal operation of the apparatus, and a second passageway of` said second heat exchanger being connected to a second passageway of said ilrst heat exchanger, a by-pass extending from the` connection between the expansion engine and the second heat exchanger to the second passageway in the second heat exchanger, whereby 10 flow of fluid from the engine passes through the second heat exchanger and returns to the nrst heat exchanger to ow therethrough in one passageway to eiIect cooling of the incoming compressed air in the other passageway, and a thermally actuated control valve in said by-pass responsive to an excess of liqueiied constituents of air in said fractionating and distilling means whereby said valve closes when the level of said liquefied constituents reaches a predetermined point to permit all of the air flowing from the engine to pass into the fractionating and distilling means.

8. Oxygen producing apparatus comprising a first heat exchanger having separate thermally bonded passageways in heat exchanging relation one of said passageways being for the introduction of compressed air, an expansion engine having its inlet connected to the outlet end of said incoming air passageway, a second heat exchanger having separated thermally bonded passageways in heat exchanging relation, one of which passageways is connected with the outlet from said engine and a second of which passageways is connected with a second passageway of the rst exchanger, a by-pass leading from the connection between the outlet of said engine and the second heat exchanger to the said second passageway of the second exchanger whereby the incoming air after passing through the first heat exchanger and engine is returned through the second exchanger to the first exchanger and discharged therefrom, a fractionating column beyond said second exchanger, conduit means extending from the connection between the first exchanger and expansion engine to the top of said column including a third passageway in said' second heat exchanger, and a thermally actuated valve in said conduit means responsive to the temperature conditions of the exhaust iluid of said engine; the said valve being opened when the temperature of said exhaust uid reaches a degree whereat the air in said third passageway becomes liquid, to permit flow of said liquid air to said column.

9. Oxygen producing apparatus comprising a rst heat exchanger having separate thermally bonded passageways in heat exchanging relation one of said passageways being for the introduction of compressed air, an expansion engine having its inlet connected with the outlet end of said incoming air passageway, a second heat exchanger having separated thermally bonded passageways in heat exchanging relation with one of its passageways connected with the outlet of said engine and a second of its passageways connected with a second passageway of the first exchanger, a by-pass leading from the connection between the engine and the second exchanger to the said second passageway through the second exchanger, a thermally actuated valve in said by-pass, a fractionating column having a boiler and a coil therein connected with the first said passageway of the secondexchanger, a conduit leading from the connection between the first heat exchanger and the engine to the top of the fractionating'column including a third passageway in the second exchanger, a thermally actuated valve in said conduit and/responsive to the temperature of the exhaust fluid of said engine and adapted to be opened when the temperature of said exhaust fluid is such that liquid air forms in the said third passageway whereupon the said liquid air flows to the top ing a predetermined level therein, to eiect a temperature condition which actuates the valve in the by-pass whereby said valve in the bypass is closed to cause the air leaving the engine to iiow through the second exchanger to a coil in the boiler of the fractionating column, the resulting increase of temperature of the exhaust iluid of the engine effecting closure of the said valve l in the conduit, a connection between saidboiler coil andthe top of the column wherebyLthe A liquid air formed in said boiler' coil 4ows to the top of the column, and a connection from .the top of said column to the second exchanger for ow` of eiiluent from the column through the second exchanger and thence through the first exl changer. c U Y 10. Oxygen producing apparatus comprising a rst heat exchanger, an expansion engine, a second heat exchanger and a fractionating i column having a coilat its base, connected in secolumn including an expansion device whereby said liquid air at reduced pressure is admitted to the column for rectication resulting in the accumulation of fractionated liquefied product liquefied product comprising a conduit having its opening from said column at the said level and having its end remote from said column in thermal relation to the rst heat exchanger so that if the accumulation of liqueed product tends to exceed said level the excess of liqueed product ows in said conduit to the end adjacent in the base' of said column about said coil, means for'inaintaining a predetermined level of said said iirst heat exchanger to be there vaporized 11. Oxygen producing apparatus comprising a and returned through said conduit to the column 1 -in gaseous form.

heat exchanger to which compressed air is inof fractionated liqueed product in the base of said column, and means preventing said accumulation beyond a predetermined level comprising a conduit"l connected to said base at;the said leveland extending to a Vregion adjacent the first heat exchanger whereat heat from the ex-A changer will vaporize said liqueiied product iiowl troduced and a fractionating column wherein said air is rectied to provide an accumulation Y ing insaid conduit from said base; the gaseous product thus formed returning to the column through said conduit in counterilow to the liquei iled product therein.

12. Oxygen producing apparatus comprising a ilrst heat exchanger having a passageway for iniiow of compressed air and having another' passageway in thermal relation to the air passageway for outflow of uid, an expansion engine having its inlet connected with the outlet of said air passageway and having its outlet connected to a second heat exchanger, said second exchanger having three separate passageways in thermal relation with one' another with one passageway having one end connected with the outlet of said engine andvwith a second passageway having its corresponding end connected with the outflow passageway of the rst exchanger and having its opposite end connected with the outlet of the engine, a thermally actu- 76 page 6l.

ated valve in the last said connection, said valve being adapted to remain open during any cooling-down `period of the apparatus to permit the air to ow from said engine to the passageway of thersecond exchanger that is connected with the outflow passageway of the ilrst exchanger, y

whereby the apparatus `is cooled down by the iiow of the air through the two heat exchangers and the expansion engine, a fractionating column, a conduit extending from theconnection between the air passageway and the inlet to the engine through the third passageway and to the fractionating column, a thermally actuated valve in said conduit responsive to `the 'temperature of,l the exhaust uid flowing from said-engine; the last said valve being opened upon the ap- -paratus being cooled down sumciently to eilect liquefaction of the air in said third passageway, whereupon said liqueiled airy can flow into the s aid column. v

13. Oxygen producing apparatus comprising a iirst heat exchanger having a passageway for inflow of compressed air and having 'another passageway in thermal relation to the air passageway for outow of uid, an expansion engine having its inlet connected with the outlet.

of said -air passageway and having its outletl connected to a second heat exchanger, said second exchanger having separate passageways in thermal relation with one another with one passageway having its warm endconnected with the outlet ofsaid engine and with its opposite end connected with a coil in the base of a fractionating column, and with another passageway having its warm end connected with the outow passageway of` the rst exchanger and having its .opposite end connected with the outlet of the engine, a thermally actuated valve in the last said connection, the said valve being adapted to remain open during any cooling-down period of said apparatus to permitthe air to flow-from said engine to the passageway of the second exchanger that is connected with the outflow passageway of the firstexchanger, whereby the apparatus is cooled downby the ilow of the air through the two heat exchangers and thev expansion engine,. and being actuated to closed position by the action of the temperature of the liquefied constituentsy of air accumulating in the base of the fractionating column during con- Vtinued operation of the apparatus.

SAMUEL-c. comms. HOWARD o.. McMAHoN.

REFERENCES CITED v The following referencesl are of record in the i'lle of this patent:

UNITED STATES PATENTS OTHER REFERENCES Development in Oxygen Production, by Rushton and Stevenson in Transactions American Institute AChemical 'Engineers February 1947, 

1. APPARATUS FOR LIQUEFYING AND SEPARATING COMPRESSED MIXED GASES, COMPRISING A HEAT EXCHANGER WHEREIN SAID MIXED GASES ARE PASSED IN HEAT EXCHANGE RELATION WITH A COLD FLUID, AN EXPANSION ENGINE CONNECTED TO SAID HEAT EXCHANGER TO RECEIVE AND EXPAND THE MIXED GASES, FRACTIONATING MEANS CONNECTED TO THE EXHAUST OF SAID ENGINE TO RECEIVE THE EXPANDED MIXED GASES, CONDUIT MEANS LEADING FROM SAID FRACTIONATING MEANS TO SAID HEAT EXCHANGER TO PROVIDE SAID COLD FLUID THERETO, A BYPASS LEADING FROM SAID EXHAUST OF SAID ENGINE TO SAID CONDUIT MEANS WHEREBY SAID EXPANDED MIXED GASES FLOW TO AND THROUGH SAID HEAT EXCHANGER IN HEAT EXCHANGE RELATION WITH SAID MIXED GASES, AND A THERMALLY ACTUATED CONTROL VALVE IN SAID BYPASS ACTUATED BY LIQUID FORMED IN SAID FRACTIONATING MEANS, WHEREBY SAID VALVE IS ACTUATED INTO CLASED POSITION BY THE TEMPERATURE OF SAID LIQUID TO PERMIT ALL OF SAID EXPANDED MIXED GASES TO FLOW INTO SAID FRACTIONATING MEANS. 